In general, a permeable concrete comprises aggregates of the size generally less than 13 mm to maintain suitable porosity and strength, and is used as a material for pavement allowing water to seep into the ground through a surface layer and a base layer of the pavement. Specifically, the permeable concrete allows rain or water to seep into the ground through pores among the aggregates, fostering the growth of trees and plants, and also helps prevent flooding of the river by allowing heavy or torrential rain to flow under the earth. Further, because the rain or water does not stay on the permeable concrete pavement, it provides less slippery and much safer walking, jogging or driving conditions.
For these reasons, the permeable concrete pavement has come into use more widely, especially on trails at parks, bicycle paths, tracks for in-line skating, golf-course trails, etc.
Conventional permeable pavements are divided into permeable asphalt concrete and permeable cement concrete. However, the asphalt concrete has disadvantages in that the surface deforms considerably due to high temperatures during the summer season and the pores get clogged up due to the viscosity of the asphalt. Also, the cement concrete is so rigid that people can hurt when they fall on it.
In addition, the conventional permeable concrete pavement is covered with epoxy pigments for cosmetic view of the surface, but a ramp covered with such epoxy pigments is more slippery than normal concrete pavement, causing problems in safety.
Further, because the surface of the concrete pavement is rugged, the surface can peel or break off, and when the pores are covered with dust, the pavement's permeability deteriorates, requiring additional maintenance costs for declogging the pores, i.e. removal of the dust.
As an example to improve the disadvantages of the conventional permeable concrete, Korean Patent No. 404679 (patented on Oct. 27, 2003 entitled “pavement using waste tire chips”) discloses an elastic permeable pavement which comprises a land layer, a filter layer, a rubble layer, a permeable concrete layer, a waste-polyurethane chip layer, and a surface layer from the bottom to the top. Specifically, the filter layer is constructed by spreading small aggregates (sand), and the rubble layer is constructed by pouring and hardening concrete rubbles of the particle size 25 mm or less onto the filter layer. The permeable concrete layer is made by blending aggregates of the particle size 5–13 mm, cement and admixture products with water, and pouring this mixture on the rubble layer and curing it. As a result, the permeable concrete layer has the compressive strength of 100 kg/cm2 or more and the permeability coefficient of 1×10−3 cm/sec or more. Further, the waste-tire chip layer is formed by pouring and spreading in the thickness of 10–20 mm a mixture including waste-tire chips of particle size 2.5–7 mm; a binder comprising 10–25 g of urethane resin, epoxy resin or acrylic resin based on 100 g of the waste tire chips; and 1–4 g of an inorganic pigment on the same base. Furthermore, the surface layer is colored by spraying with the urethane resin, epoxy resin or acrylic resin on the waste-tire chip layer.
The elastic permeable pavement as disclosed in the above patent allows rain or water to penetrate into the ground, and the pavement is resistant to slipping and reduces diffused light-reflection resulted from the water staying on the pavement, thus securing safe passage of pedestrians and providing comfortable vision. Also, as using waste tires which have been one of the environmental pollutants, the pavement not only absorbs impact on foot, but also contributes to the protection of environment and recycling of resources.
However, since the waste tire's smell of rubber lasted for a long time, the pavement using the waste tire could not provide a pleasant sense of smell. Further, since the urethane, epoxy and acrylic resin binders used in the above patent were those available in the market, there have been demands for a special binder which enhances the adhesive strength among pavement materials and maintains the strength and durability of the pavement for a long time.
Accordingly, the inventor of the present invention studied and researched into materials and binders for the elastic permeable pavement, and as a result, the inventor completed the present invention by using waste-polyurethane chips in place of waste-tire chips as a main component of the elastic pavement and developing a binder to secure the binding between an upper polyurethane-chip layer and a lower permeable-concrete layer as well as the binding among the waste-polyurethane chips.